An apparatus of this type is described, for example, in DE-A 42 06 166. There, the two members are coupled through pistons which are arranged along the circumference and which can be moved radially in the coupling direction from the outside towards the inside via hydraulic fluid in opposition to the biasing force of an annular spring. For decoupling, the annular spring moves the respective pistons radially outwardly, counteracting the hydraulic pressure behind an annular surface separating the two members. Disadvantageously, however, the apparatus described in the above referenced patent document exhibits problems in conjunction with switching times, in particular at low temperatures when the hydraulic fluid has a high viscosity. If the internal combustion engine is started at relatively low ambient temperatures, the viscosity of the hydraulic fluid can be so high that the spring unit cannot move the piston into the decoupled position during the time available for the decoupling process (base circle). Such switching problems occur in particular when the internal combustion engine is operated not only at low ambient temperatures, but-after starting-also in a speed range above the idle speed, for example at partial load or even full load.